1. Field Of The Invention
In general, the present invention relates to systems and methods that are used to reduce the mutagenicity associated with aromatic extracts that are produced during the refinement of petroleum oils. More particularly, the present invention relates to processes that temporarily combine aromatic extracts with materials that separate, remove, and/or reduce mutagenic compounds from petroleum aromatic extracts.
2. Prior Art Description
In the distillation of certain petroleum oils, aromatic extracts are produced. Aromatic extracts are typically produced during the refining of lubricating oil basestocks and waxes. Aromatic extracts are solvent extracts of distillates or the residue (residuum) from a refinery vacuum tower. Aromatic extracts are complex, highly viscous liquids that contain predominately aromatic hydrocarbons covering the carbon number range of C15 to C50.
Aromatic extracts can be grouped into two subcategories, which are distillate aromatic extracts (DAEs) and residual aromatic extracts (RAEs), according to the class of lubricating oil feedstock from which they are derived. The aromatic extracts are used as blending components of heavy fuels and in the manufacture of rubber and plastic. Aromatic extracts are also used as feedstock for production of carbon black, petroleum pitches, and resins.
Aromatic extracts contain certain levels of known mutagenic compounds. For example, distillate aromatic compounds contain significant amounts of polycyclic aromatic compounds, which are known mutagens. As a consequence, the use of distillate aromatic extracts as extender oils has been prohibited in the European Union beginning in January of 2010. Residual aromatic extracts (RAEs) can still be used, but must meet certain regulatory specifications.
Mutagenicity is a primary safety concern with the use of petroleum oils. However, the amount of mutagenic compounds present in a petroleum oil being processed varies from lot to lot. Each processed lot must be tested for levels of mutagenic compounds prior to being released by the refinery. Lots that meet regulatory specifications can be released. Lots that do not meet the regulatory specifications cannot be released and must be reprocessed by the distillery or disposed of as toxic waste. The holding and reprocessing of aromatic extracts adds significantly to the costs associated with running a petroleum refinery.
A particular lot of aromatic extracts is said to meet regulatory specifications by passing a biological mutagenicity test. The most common such test utilizes a salmonella/microsomal activation mutagenesis assay and is commonly referred to as the Modified Ames Test, or ASTM Method E 1687. Such a test produces a mutagenicity index (MI) ranking for the aromatic extracts being tested. For use in the European Union, residual aromatic extracts must have mutagenicity indices (MIs) of less than 0.40 in this assay.
The production run of aromatic extracts cannot be released by the refinery until the test results are received. This requires that the aromatic extracts be stored at the refinery. Furthermore, production runs of aromatic extracts have a high failure rate. If a production run fails, the aromatic extracts must be further processed. This significantly increases the costs of production.
In the prior art, there are several processes used by refineries to isolate or reduce the level of mutagenic compounds in petroleum byproducts. Many of these processes require the material to be mixed with virgin stock and reprocessed. This greatly reduces the productivity of the refinery since material must pass through refinery equipment more than once. In other processes, compounds can be added to the petroleum by products that isolate or reduce the mutagenic compounds. For example, in U.S. Pat. No. 6,010,617 to Mackerer, the mutagenicity of coal tar derivatives are reduced by mixing the coal tar derivatives with an alkylation agent.
In the present invention, a simple ketone is used as one agent to reduce mutagenicity in aromatic extracts of petroleum oils. Simple ketones, such as acetone, have often been mixed with petroleum oils in refineries. However, the use of the ketone is for the purpose of thinning the petroleum oil so that it flows better through the piping of the refinery. Such prior art is exemplified in U.S. Pat. No. 2,220,016 to Lyons, U.S. Pat. No. 2,096,950 to Wilson, and U.S. Pat. No. 3,052,620 to Hanson. Although such prior art mixes acetone with the feedstock oil, the acetone is evaporated in the distillation tower of the refinery prior to the creation of the aromatic extracts.
A need therefore exists for a system and method of treating aromatic extracts at a refinery to reduce mutagenicity indices in production lots of residual aromatic extracts so that all such lots pass current safety standards. Moreover, a need also exists for a system and methodology that reduces the mutagenicity indices of distillate aromatic extracts to levels where those oils would be deemed safe according to current standards, therein allowing distillate aromatic extracts to be once again used as process oils. These needs are met by the present invention as described and claimed below.